1. Field of the Invention
The present invention concerns a method for acquisition of angiographic data sets from a region of an examination subject, as well as a magnetic resonance system for acquisition of such data sets.
2. Description of the Prior Art
Angiography is a known medical diagnosis method in which blood vessels are shown by means of diagnostic imaging methods. For example, x-ray or magnetic resonance tomography methods can be used for this purpose. In magnetic resonance (MR) tomography, for example, the imaging is sensitive to the movement of nuclear spins that generate the MR signal. These effects can be used to acquire angiographic images, i.e. images of the vessels of the examined person. Angiographic techniques that are based only on the flux effects of the spins located in the body are known for this. Furthermore, contrast agent-supported MR angiography (ceMRA) is a method frequently applied in clinical practice. With this modality, primarily large vessels can be shown without ionizing radiation.
In contrast agent-based MR methods it is desirable to increase the spatial resolution, which can be achieved via longer scan times, for example. The scan times are limited, however, because the contrast agent supplied to the bloodstream of the patient passes into the tissue, so the blood/tissue contrast is reduced. This effect can be reduced by the use of blood pooling agents. Contrast agents of high molecular weight are thereby administered that remain in the blood longer and cause a lesser tissue contrast. An additional problem that particularly occurs given a selective presentation of arteries or veins, is then moved into the foreground by the use of such contrast agents. If a contrast agent is added to the bloodstream for an imaging of the arteries, the veins in the examined region also additionally contrasted given a longer scan duration. In angiography, for the image data for every shown vessel, it must retroactively be decided whether it is an artery or vein, so the evaluation of the acquired image data is made significantly more difficult and a considerable time cost is incurred. This problem particularly occurs in pelvic/leg angiography on the lower leg, since here the vessels are relatively small and veins and arteries run in parallel. A high spatial resolution (therefore also a long scan duration) is thus required due to the size of the vessels; but a differentiation of arteries and veins is hampered since an artery is accompanied by two veins. Since it is not possible to establish the arrival of the venous contrasting in conventional magnetic resonance systems, the magnetic resonance data sets that are used for reconstruction of image data are normally data sets from the arterial phase and the venous phase. The reconstructed image data consequently depict both arteries and veins and a manual differentiation is necessary, which is difficult to conduct, in particular in the case of pelvic/leg angiography.